The effect of Vitamin A on immune responses

Under physiological conditions, tolerance to commensal bacteria is maintained through the induction of regulatory T cells that suppress immune responses. Central to this immune response modulation is retinoic acid, the active metabolite of vitamin A.

Scientists on the EU-funded RA AND GD T CELLS (The effect of retinoic acid on the fate of γδ T cells) project wished to extend these findings to γδ T cells that defend the mucosal surfaces of the body against infection but also play a crucial role in autoimmunity. The inherent capacity of these cells to rapidly switch from a pro-inflammatory to an anti-inflammatory state and vice versa, strongly affects the outcome of the immune response. Importantly, γδ T cells have the capacity to be self-reactive, and therefore, influence the development of autoimmune diseases.

To elucidate the role of vitamin A on γδ T cells, scientists isolated these cells from the lymph nodes, spleen and skin of mice. They observed that retinoic acid had an overall suppressive effect on γδ T cells and inhibited their capacity to differentiate, proliferate and respond to pathogenic stimuli. Treatment of a mouse model of multiple sclerosis with retinoic acid significantly reduced disease symptoms, and decreased the frequency and activity of the autoreactive γδ T cells as well as the CD4 helper T cells responsible for neuroinflammation. Interestingly, treatment of this single cell type with retinoic acid was enough to prevent immune cells from transferring diseases to recipient mice.

Collectively, the findings of the study demonstrate that retinoic acid has powerful anti-inflammatory properties in a model of multiple sclerosis by suppressing the pathogenic function of γδ T cells. Given the role of γδ T cells in a number of autoimmune diseases, simple dietary interventions involving vitamin A-rich foods may help to re-set the immune imbalance in such patients.